1. Field of Invention
Psoralens, photochemotherapy, psoralens having enhanced photosensitizing activity for use in photochemotherapy.
2. Prior Art
Psoralens have been used for years as dermal photosensitizing agents, e.g., in the treatment of vitiligo. Their topical and/or oral application, followed by irradiation with light, results in stimulation of melanin, thus producing a tanning effect. They have accordingly also been used for such cosmetic purpose. More recently, psoralens have been found useful in the photochemotherapeutic treatment of psoriasis, in which case they are administered orally or topically to the subject, whose skin is subsequently exposed to controlled ultraviolet radiation, as in a Psoralite (.TM.) apparatus. A high percentage of remissions of this disease have been effected in such manner.
The effectiveness of a psoralen for such uses and for such purpose is at least partially related to its ability to produce erythema upon the skin upon irradiation. Psoralens also have other uses, and their uses, as well as underlying rationale and theory, are partially elucidated in U.S. Pat. No. 4,124,598, and are otherwise well-known in the art from various preexisting publications.
With the increasing emphasis on photochemotherapeutic treatments for various purposes using psoralens and controlled application of ultraviolet light, the requirements for optimally-effective photosensitizing psoralens have become more apparent. To eliminate the necessity of excessive and perhaps dangerous ultraviolet light applications or dosages, maximum photosensitization is one obvious criterion. However, to eliminate excessive periods of waiting before photochemotherapy can be commenced, rapid onset of photosensitization upon topical or oral administration of the photosensitizing agent is also of significance. Long or extended action is another criterion of significance in some cases, as when irradiation cannot be applied without some period of delay. Thus, the criteria of rapid onset, early maximization, and extended period of photosensitization action or effect are established as desirable criteria for the photosensitizing agent in this relatively new but rapidly-expanding field of photochemotherapy, certainly of equal importance as contrasted to the single previously-important criterion of high maximum photosensitization activity alone.
The recently-developed 4'-aminomethyl-4,5',8-trimethylpsoralen appears to be characterized by a high order of oral photosensitizing activity, but exhibits a high degree of toxicity. A low toxicity is, of course, essential. The compounds 5'-aminomethyl-4'-methylpsoralen and 8-aminomethylpsoralen, on the other hand, are essentially inactive orally, apparently due to absence of the 4-methyl group, thus making the photosensitizing activity even more unpredictable than ever in the area and immediate vicinity of the present invention.